Monolithic Two-Dimensional Optical Fiber Array

ABSTRACT

A two-dimensional (2D) optical fiber array component takes the form of a (relatively inexpensive) fiber guide block that is mated with a precision output element. The guide block and output element are both formed to include a 2D array of through-holes that exhibit a predetermined pitch. The holes formed in the guide block are relatively larger than those in precision output element. A loading tool is used to hold a 1×N array of fibers in a fixed position that exhibits the desired pitch. The loaded tool (holding the pre-aligned 1×N array of fibers) is then inserted through the aligned combination of the guide block and output element, and the fiber array is bonded to the guide block. The tool is then removed, re-loaded, and the process continued until all of the 1×N fiber arrays are in place. By virtue of using a precision tool to load the fibers, the guide block does not have to be formed to exhibit precise through-hole dimensions, allowing for a relatively inexpensive guide block to be used.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/011,370, filed Jan. 29, 2016 and herein incorporated by reference.

TECHNICAL FIELD

The present is vention relates to a two-dimensional optical fiber arraycomponent and a method for constructing an array component in a mannerthat provides the required alignment tolerances while minimizingcomponent cost and reducing the assembly complexity.

BACKGROUND

Optical communication systems, particularly those associated withtelecommunications and data center applications, face an ever-increasingneed for larger optical switching configurations, such as opticalcross-connects and “fiber-to-free-space” switching fabrics. Theinterconnectivity of devices via Internet-based cloud computing, as wellas cloud storage capabilities, has raised the demand for lower costoptical communication systems that are able to easily and quickly switchsignal paths.

Optical routing of one path of an N×N array of input ports to any otheroutput port of an N×N array of outputs will be further enabled by thedevelopment of a readily producible two-dimensional (2D) fiber arraycomponent that is available for a relatively low cost. In suchfree-spacing routing paradigms, an N×N fiber array is disposed at theback focal plane of an N×N lens array, which produces beams with theirminimum waist between the communicating arrays. The routing function isenabled, for example, by a pair of properly-placed, two-dimensional MEMSarrays that allows any input to be switched to any output. FIG. 1illustrates an exemplary structure for providing this function. Notethat the optical arrangement is typically a conjugate imaging system sothat a position error of the fiber at the input will be beam positionerror at the output fiber. Very small changes (i.e., on the order of amicron) create large insertion loss errors. This type of error is oftenreferred to as a positional error related to variations in thecenter-to-center spacing between the core regions of adjacent opticalfibers in the array (hereinafter referred to as “pitch”).

Besides the inter-fiber spacing (pitch) inaccuracies, error in thepointing of the beam as it exits a fiber will produce a displacement ofthe output beam that can create coupling loss, clipping, and scatterednoise problems. FIG. 2 illustrates this “pointing error” for anexemplary optical fiber 1, as positioned through an aperture 3 formed ina substrate 4. As shown, optical fiber 1 passes through aperture 3 in anoff-axis manner, creating an angular amount of fiber tilt (θ), measuredwith respect to a normal of an exit surface 2. This measure θ is definedas the angular pointing error. While shown in this case as maintainingits optical axis, insertion of optical fibers through apertures may alsoresult in the fiber experience some amount of bending, also creatingangular pointing error at the output. Fiber and thus bean pointing errorimpinging onto a collimating lens produces an output beam that isdisplaced relative to the optical axis of the system. To accommodatethis displacement (so as to avoid clipping, scattering, and cross-talk),the MEMS micro-mirrors would need to increase in size, with theundesirable effect of reducing their density or increasing thecomplexity of the MEMS design. Thus, problems associated with creatingfree-space optical cross-connections, in high volume resides with the 2Dfiber array requiring a low pitch error, as well as a low pointingerror. Today's applications for such a switching fabric havesimultaneous requirements of a pitch error on the order of ±1 μm orless, and a pointing error on the order of ±15 mrad (or smaller).

To date, one approach to improve the 2D fiber array component is basedupon the utilization of a multiple number of precisely-etched (tapered)silicon wafers, each wafer formed to include progressively smaller andmore accurately aligned vias, which may require high hole aspect ratios(i.e., the ratio of the side wall straight length to the hole diameter).The cost of fabricating multiple silicon wafers with different-sizedvias, and then manipulating a stack of these wafers to align the vias isprohibitive from a cost point of view (although the required, precisealignment may be achieved). Furthermore, it is more costly and difficultto produce high aspect ratios as previously described. Locatingindividual wafers farther from each other axially can help addresspointing error issues, but increases the difficulty of assembly of such2D arrays, and ultimately increases the cost.

In another approach, only a pair of wafers is used, where their vias arealigned and then fibers are inserted one at a time (or one 1×N fiberarray at a time) and positioned to create the desired alignment. Here,the assembly time is significant and cumbersome, again resulting in anexpensive process. Additionally, since each element of thisconfiguration is a precisely made component, the final structure can becostly.

U.S. Pat. Nos. 6,470,123 and 6,766,086 are illustrative of these priorart techniques. U.S. Pat. No. 6,470,123, which issued to Sherman et al.on Oct. 22, 2002, describes a high density optical fiber array assemblyand assembly method that utilizes a series of separate, stacked guideplates that form a series of fiber guide channels. The guide plates arestacked within a housing so that the bottom of one acts as a cover forthe channels of another. The fiber arrays can be “tool inserted” alongthe channels as one group, such as a row of fibers, or manually insertedone at a time and advanced sequentially. U.S. Pat. No. 6,766,086, whichissued to Sherman et al. on Jul. 20, 2004 describes an optical fiberarray apparatus comprising a housing front mask having a matrix of fiberseating openings, with each opening having one or more side walls. Anoptical fiber extends through each opening and a tool is used to pressthe fiber side surface into engagement with the one or more side wallsto precisely position and secure the fiber. Bonding material then fillsall voids in and around the opening. In one embodiment, a clamping waferbehind the front mask moves to clamp the fibers to the front maskopening walls. In another, the front mask defines flexing arms withdistal ends that clamp fibers to opening walls and in yet anotherelongated flexible members lie along front mask slots to clamp fibers inopenings that communicate into the slots.

SUMMARY OF THE INVENTION

The needs remaining in the prior art are addressed by the presentinvention, which relates to a two-dimensional optical fiber array and amethod for constructing an array in a manner that provides the necessaryalignment requirements while minimizing component cost and reducing theassembly complexity, especially in higher N×N 2D fiber arrays.

In accordance with the present invention, a two-dimensional (2D) opticalfiber array component takes the form of a monolithic fiber guide blockincluding a 2D configuration of through-holes that mates with aprecision output element of the same 2D aperture configuration. Thethrough-holes of the fiber guide block are arranged to exhibit thepredetermined pitch of the system being assembled. While having thepredetermined pitch, the diameter of each individual through-holes inthe fiber guide block is relatively large (i.e., slightly greater thanthe diameter of a coated optical fiber), simplifying the process ofloading 1×N fiber arrays into the guide block. The precision outputelement is positioned over and aligned with respect to the fiber guideblock, so that as a 1×N fiber array is loaded, the stripped end portionsof the fibers will exit through the apertures at output surface of theprecision output element. A loading tool is configured to hold aplurality of N separate fibers in a spaced-apart arrangement thatmaintains the predetermined pitch. Therefore, as a 1×N array of fibersis loaded into the array component, this precision pitch (as defined bythe tool) is maintained as the fibers pass through the largerthrough-holes of the guide element and then through theprecisely-configured apertures (also referred to as “vias”) at theoutput element. After each 1×N fiber array is loaded, an epoxy (orsimilar material) is used to attach the loaded 1×N fiber array to thebackside of the fiber guide. Once fixed in place, the fiber loading toolis removed and re-loaded with another plurality of N fibers and theprocess is repeated until the 2D array component is fully loaded withfibers.

Inasmuch as the fiber guide block does not need to exhibit the precisealignment tolerances (pitch and pointing) demanded for the final outputof the 2D array structure, a relatively low-cost material andmanufacturing process can be used in the fabrication of this element ofthe structure. For example, a plastic material may be used.

In one embodiment of the present invention, the precision output elementcomprises a multilayer silicon-based structure including an inputsilicon layer (having etched vias) and an output silicon layer (alsoincluding etched vias), with a spacer element (also of silicon) disposedbetween the input and output layers. The silicon spacer is used asstructural support for the output structure, ensuring that the opticalfibers passing through the vias do not bend or shift (which would createpointing errors). Additionally, the silicon spacer may be configured toinclude over-sized relief holes (when compared to the vias in the inputand output layers) so that any adhesive used to affix the fibers to theoutput layer will pool within the silicon spacer and not further travelalong the fiber. Other configurations of a multilayer silicon-basedoutput element may include additional layers (or fewer, such aseliminating the spacer), as the case may be.

Other materials may be used in the formation of the precision outputelement, as long as the element exhibits a coefficient of thermalexpansion (CTE) that is relatively low, allowing for the element tomaintain its required pitch and pointing error requirements over a giventemperature range, and in the presence of any possible environmentalconditions.

An exemplary embodiment of the present invention takes the form of atwo-dimensional (2D) array component for supporting a plurality ofindividual optical fibers in a 2D configuration exhibiting apredetermined pitch, the array component comprising a fiber guide blockincluding a plurality of through-holes arranged in a 2D arrayconfiguration, the plurality of through-holes disposed to exhibit thepredetermined pitch, each through-hole having a diameter on the order ofa coated optical fiber; a precision output element including a pluralityof apertures arranged in the 2D array configuration, the plurality ofapertures disposed to exhibit the predetermined pitch, each aperturehaving a diameter on the order of a stripped optical fiber; and amounting flange for supporting the fiber guide block and the precisionoutput element in an aligned configuration such that a 1×N array ofpre-aligned optical fibers may be inserted through a rear opening of themounting flange and exit from the precision output element in aconfiguration that exhibits the predetermined pitch with a minimalpointing error.

Another embodiment of the present invention is defined as a method ofassembling a two-dimensional (2D) optical fiber array component toexhibit a predetermined pitch, with a predetermined minimum pointingerror, including: providing a fiber guide block that includes aplurality of through-holes disposed in the defined 2D pattern, theplurality of through-holes positioned to exhibit the predetermined pitchand each through-hole having a diameter slightly larger than a coatedoptical fiber; providing a precision output element that includes aplurality of apertures disposed in the defined 2D pattern, the pluralityof apertures positioned to exhibit the predetermined pitch, with eachaperture having a diameter on the order of a stripped optical fiber;providing a mounting flange with a sleeve opening; inserting the fiberguide block into the mounting flange sleeve opening; inserting theprecision output element in the mounting flange sleeve to overly thefiber guide block in a manner such that the plurality of apertures alignwith the plurality of through-holes; loading a plurality of N strippedoptical fibers onto a precision tool that is capable of holding theplurality of N stripped optical fibers in a 1×N array with thepredetermined pitch, creating a pre-aligned 1×N array of optical fibers;inserting the precision tool through a backside opening in the mountingflange and directing the 1×N array of pre-aligned optical fibers througha 1×N array of through-holes in the fiber guide block and an aligned 1×Narray of apertures in the precision output element until stripped endterminations of the plurality of N stripped optical fibers exit from theoutput element; attaching the inserted 1×N array of fibers to a backsideof the fiber guide block to fix and maintain the desired pitch andpointing error of the loaded 1×N array; repeating the steps of loading,inserting, and attaching until an entire 2D array of optical fibers isin place; and bonding the exposed stripped end terminations of the 2Darray of optical fibers to an outer surface of the output element.

Other and further aspects and embodiments of the present invention willbecome apparent during the course of the following discussion and byreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings,

FIG. 1 illustrates an exemplary optical communications environmentwithin which a switching fabric utilizing a two-dimensional opticalfiber array may be used;

FIG. 2 is a diagram illustrating the particular details associated withpointing error;

FIG. 3 is an isometric view of an exemplary 2D fiber array componentformed in accordance with the present invention;

FIG. 4 is top view of a portion of the embodiment of FIG. 3;

FIG. 5 is an enlarged view of a portion of FIG. 3;

FIG. 6 is a side view of a portion of an output element, illustratingthe potential for pointing error when not implementing the features ofthe present invention;

FIG. 7 is an isometric view of an exemplary multilayer silicon-basedversion of the precision output element of the 2D fiber array component;

FIG. 8 is a cut-away side view of a portion of an exemplary embodimentof a 2D fiber array component formed in accordance with the presentinvention;

FIG. 9 is an exploded isometric view of an exemplary configuration ofthe present invention, illustrating fiber strain relief elements as usedin conjunction with the 2D fiber array component;

FIG. 10 illustrates the elements of FIG. 9 in an assembled form;

FIG. 11 contains an exploded view of an alternative embodiment of thepresent invention, in this case combining the fiber guide block with themounting flange;

FIG. 12 is a view of a top surface of the mounting flange shown in FIG.11, including an exemplary output element that mates with the topsurface;

FIG. 13 is an isometric view of the rear (entrance) face of the mountingflange as shown in FIG. 11, illustrating a process for loading 1×N fiberarrays into the through-holes formed directly in the mounting flange;and

FIG. 14 is a flowchart illustrating an exemplary method for assembly a2D fiber array component formed in accordance with the presentinvention.

DETAILED DESCRIPTION

As briefly mentioned above, FIG. 1 illustrates a typical opticalcommunication switching system 10 that may utilize the monolithic 2Dfiber array component of the present invention. As shown, switchingsystem 10 provides “fiber-to-free-space” switching between a first 2Dfiber array 12 and a second 2D fiber array 14 via associated lens arrays16, 18 and MEMS arrays 20, 22. Each fiber array includes a plurality ofindividual optical fibers 24, separated by a predetermined spacing(hereinafter referred to as “pitch”) and coextensive with the surface ofthe array to direct light beams in a direction perpendicular to thearray surface (pointing, as discussed above in association with FIG. 2).

Referring to first 2D fiber array 12, fibers 24 are shown as beingintroduced through the back side of an array substrate 26 anddistributed in an array configuration (here, a 4×4 array). Arraysubstrate 26 is formed such that the endfaces of the inserted fibersalign with a set of individual lenses 28 formed in lens array 16,providing collimated output signals that are thereafter directed towardMEMS array 20. After being re-directed through MEMS arrays 20 and 22,the signal(s) pass through lens array 18 and is/are received at second2D fiber array 14.

The actual progress of optical signals back and forth through switchingsystem 10 is well known in the art and is not germane to the subjectmatter of the present invention. As mentioned above, the presentinvention is directed to an improved structure and assembly for a 2Dfiber array that maintains the necessary alignment with the lens arraysand MEMS arrays in a low-cost configuration. While various techniqueshave been developed to minimize the cost and size of the othercomponents forming switching system 10 (e.g., MEMS array, lens array),the structures and assembly methods used to interconnect the actualoptical fibers with the remaining switch components have remainedexpensive, labor-intensive processes.

Accordingly, the present invention provides a monolithic fiber arraystructure that reduces the overall size and complexity of the arraycomponent, retaining the desired alignment tolerances, pitch andpointing, while also simplifying the assembly of the configuration.

FIG. 3 is an exploded view of an exemplary 2D fiber array component 30formed in accordance with an embodiment of the present invention. Arraycomponent 30 includes a monolithic fiber guide block 32 and a precisionoutput element that are held in an aligned configuration within amounting flange 38. A precisely-configured tool (not shown) is used toload pre-aligned 1×N fiber arrays 100 through a rear opening 46 ofmounting flange 38, with the end terminations of the fibers being threadthrough through-holes 33 formed in fiber guide block 32 and apertures 36formed in precision output element 34 (through-holes 33 exhibiting thesame pitch as apertures 36, but of a somewhat larger diameter). As willbe discussed in detail below, apertures 36 are formed in a pre-defined2D array pattern that creates the pitch, while minimizing pointingerror.

As shown, mounting flange 38 includes a sleeve 40 with a first shoulder42 for supporting fiber guide block 32 as it is inserted into sleeve 40.A second shoulder 44 is formed in sleeve 40 and is used to supportoutput element 34 over guide block 32 in a spaced-apart arrangement withalignment between through-holes 33 of fiber guide block 32 and apertures36 of output element 34. A rear opening 46 is formed in mounting flange38 and is used to accept the 1×N array of fibers 100 as they are loadedinto component 30. By virtue of presenting a pre-aligned 1×N fiber arrayto guide block 32 (via the precision loading tool), and maintaining thealignment as the fibers pass through output element 34, it is possiblein accordance with the present invention to efficiently loadprecisely-aligned fiber arrays, providing improvement over prior artconfigurations. As each 1×N fiber array is loaded, a suitable epoxy isintroduced through mounting flange 38 to affix the fibers to thebackside of guide block 32.

In contrast to some prior art configurations, the majority of elementsforming fiber array component 30 comprise low-cost materials and may beassembled used a relatively a low-cost manufacturing process. Forexample, fiber guide block 32 may be formed of a plastic material andmay be injection molded, printed using 3D technology, or manufactured inany way that easily forms through-holes 33 within the plastic piecepart.Flange 38 is typically a machined stainless steel structure, with thelocation and dimensions of shoulders 42 and 44 controlled by themachining process. Thus, the arrangement of the present invention limitsthe need for relatively expensive components (and requisite expensiveprocessing and assembly) to precision output element 34.

FIG. 4 is a cut-away top view of the exemplary fiber array component 30of FIG. 3, with FIG. 5 being an enlarged view of a portion of the viewof FIG. 4. Referring to FIG. 4, the positioning of fiber guide block 32and precision output element 34 within sleeve 40 of mounting flange 38is clearly shown. In accordance with the present invention, sleeve 40 issized and configured (along with shoulders 42 and 44) such thatpre-aligned 1×N arrays of fibers entering the arrangement at rearopening 46 will automatically align with apertures 36 of output element34 pass directly through apertures 36 without the need for any otheralignment processes). As will be described in detail below, by virtue ofusing a precision tool that pre-aligns a 1×N array of fibers to therequisite pitch, the fiber guide block does not need to exhibit asimilar level of accuracy and can be formed from a lesser expensiveprocess. The individual fibers of the 1×N array are held by theprecision tool, which is used to arrange them into the proper pitch.Since the length of the stripped fibers is relatively short, the fiberscan be held by the tool in a straight, parallel configuration withlittle pointing error at the proper pitch. With the fiber guide blockand output element pre-aligned with respect to each other, the toolholding the aligned fibers can be readily guided so that the fibers areinserted into the through-holes of the guide block, and then furtherinto the apertures of the output element without interference, for everyfiber of the 1×N array of fibers. Inasmuch as the precision tool will bere-used in the assembly of multiple fiber array components, theassociated expense in creating such a tool is relatively low on a percomponent basis.

Continuing with the description of FIGS. 4 and 5, a 1×N array of fibers100 is shown as being loaded through rear opening 46 of mounting flange38 (the precision tool used to maintain the predetermined pitch Pbetween adjacent fibers not shown). The stripped end terminations 100Eof fibers 100 are shown as exiting through precision output element 34.Once a 1×N fiber array is loaded, an epoxy E is applied along thebackside B of fiber guide block 32 to hold the fibers in fixed, alignedposition. After the epoxy is cured, the precision tool is removed andreloaded with another plurality of N fibers, again presenting apre-aligned (with respect to the desired pitch) array of fibers forloading into array component 30.

As best seen in FIG. 5, the diameter of through-holes 33 for need fiberguide block 32 is selected to be able to accommodate coated opticalfibers. The diameter of apertures 36 formed in precision output element34 is selected to be slightly greater than the diameter of claddedoptical fibers (i.e., “stripped” fibers with the coating materialremoved). In this particular configuration, precision output element 34is shown as a multilayer structure, which each layer including vias thatalign to form apertures 36. One exemplary embodiment of a multilayeroutput element 34 will be discussed below in association with FIG. 7.

Referring again to FIGS. 4 and 5, fiber guide block 32 is preferablyformed of a material that allows for the interior walls of through-holes33 to be relatively smooth. In that case, as a 1×N array of fibers isloaded, the fibers pass along unimpeded as they progress through theinterior of element 32. The ability to insert the fibers in a mannersuch that they remain “straight” assists in minimizing the pointingerror of the final structure. Suitable plastic materials exhibit thiscapability, and are also able to tolerate thermal cycling.

FIG. 6 is a cut-away side view of a portion of an exemplary precisionoutput element 34, shown in this case without an accompanying fiberguide block. It is evident in this illustration that the presence ofeven a slight bend along the length of a fiber being inserted intooutput element 34 results in creating an unacceptable amount of pointingerror at output surface 54 of output element 34. The inclusion of afiber guide block (aligned with output element 34), in conjunction witha precision tool that pre-aligns the fibers to the predetermined pitch,overcomes this pointing error problem and creates 2D fiber arraycomponent that fully meets (if not exceeds) the industry requirementsfor pitch and pointing error without requiring overly-strict and precisetolerances on the precision output element.

The existence of some pointing error in output element 34 as shown inFIG. 6 may be associated with degree of precision that is able to befabricated within the layers forming this multilayer arrangement. It maybe possible to utilize a silicon output element with deeply-etched viasin layers of sufficient thickness to achieve the pointing errortolerance. In these cases, the alignment between the fiber guide blockand the output element may not need to be as well controlled. Theinclusion of the fiber guide block provides further assurance ofalignment and also adds to the strain relief of the final arrangement.

In one exemplary embodiment of the present invention, precision outputelement 34 is formed as a multilayer silicon-based element. FIG. 7illustrates an exemplary three-layer structure including a top guidinglayer 48 and a bottom guiding layer 50 (both formed of silicon), with aspacer 52 inserted between top and bottom layers 48, 50 as shown. Spacer52 is not required by formed of silicon; any material with a similar CTEmay be used. As is well-understood in the art, top and bottom siliconlayers 48, 50 may be precisely etched using well-known semiconductorfabrication processes to create vias (i.e., etched, small diameterapertures) that ultimately present a 2D fiber array in aprecisely-aligned configuration that meets (if not exceeds) thealignment tolerances required for optical switching systems. Outersurface 54 of top layer 48 is defined as an exit surface for a 2D fiberarray component 30 utilizing this multilayer silicon-based outputelement embodiment of the present invention.

Referring to FIG. 7, a plurality of vias 56 is formed through top layer48, and another plurality of vias 58 is formed through bottom layer 50.In most cases, these vias are formed using a standard etching processtypical in semiconductor material processing. Layers 48 and 50 arealigned in a manner that also aligns the plurality of vias 56 with theplurality of vias 58. As will be discussed in detail below, spacer 52 isformed to include larger openings 60 (larger with respect to vias 56,58), referred to at times hereafter as “relief openings”.

In accordance with this particular embodiment of the present invention,top layer 48 is processed to create the plurality vias 56 with theaccuracy required to achieve and maintain the required pitch P andpointing tolerances of the array component. As mentioned above, vias 56are preferably formed to have a diameter only slightly larger than acladded fiber at output surface 54. The enlarged inset view within FIG.7 illustrates the size and spacing of an exemplary via 56, reliefopening 60 and via 58 to align and form a through-hole 36 forsilicon-based output element 34. In this particular arrangement, vias 56are shown as having a larger lead-in opening 56-O to assist in theguiding of the associated fiber through the aperture. While it ispossible to configure a precision output element with tapered apertures(in this case, with vias 58 slightly larger than vias 56), this is not arequirement and non-tapered apertures may also be used.

As best shown in the inset, spacer 52 is formed to include a pluralityof relatively large relief openings 60. In accordance with this aspectof the present invention, relief openings 60 function to inhibit epoxyflow between top layer 48 and bottom layer 50 as the terminal portionsof the fibers are fixed in place across output surface 54 of outputelement 34. Without these relief openings, fibers inserted through vias56, 58 may later be subject to “piston” action and become mis-aligned.The thickness t of spacer 52 also serves as additional structuralsupport for output component 34.

FIG. 8 is a cut-away side view of a portion of mounting flange 38 incombination with fiber guide block 32 and multilayer output element 34as described above, clearly illustrating the alignment between theopenings in the manner required to maintain pitch and minimize pointingerror, while also allowing for straightforward assembly of the fiberswith component 30. While shown as a three-layer component in FIG. 8, itis to be understood that precision output element 34 may be formed ofany suitable number of layers. Additionally, while silicon may be apreferable material useful in forming apertures from aligned vias,materials other than silicon may be used to form the multilayerstructure.

An exemplary optical fiber 100 i is illustrated in FIG. 8 as positionedthrough the complete opening formed by the aligned combination ofaperture 36 and through-hole 33. Stripped end termination 100E of fiber100 is clearly shown as exiting through outer surface 54 of multilayeroutput element 34. As mentioned above, top silicon layer 48 of asilicon-based output element 34 is fabricated to exhibit precisealignment and dimensions for the plurality of vias 56. Spacer 52 servestwo functions: (1) it forms a structural member serving to stiffen thestack so that it can be successfully polished; and (2) it forms areservoir that prevents the epoxy used to attach the fibers to topsurface 54 from wicking down to bottom layer 50. This epoxy reservoirthus eliminates the potential for fiber pistoning as a function oftemperature fluctuations.

In the particular embodiment as shown in FIG. 8, vias 58 formed inbottom layer 50 are slightly larger in diameter than vias 56 formedwithin top layer 48. The slightly larger size of vias 58 is useful inmaintaining the pre-aligned arrangement of the fibers as the loadingtool (not shown) moves the fibers forward into the tighter clearancevias 56 with sufficient “straightness” (i.e., little or no “pointing”).In the particular arrangement as shown in FIG. 8, both vias 56 and 58are formed to include larger lead-in openings (56-O and 58-O) to assistthe passing the individual fibers through the structure.

In accordance with the present invention, by virtue of using a precisionloading tool that presents the fibers in a pre-aligned configuration(i.e., with the desired fiber pitch), fiber guide block 32 requires lessprecision and therefore includes relatively large clearancethrough-holes 33. The addition of epoxy E (or other appropriatematerial) to the surface of the fibers in the vicinity of through-holes33 at the backside B of fiber guide block 32 provides an additionalmeasure of strain relief for the final structure. In particular, arelatively soft, compliant epoxy can be used to affix a sidewall portionof the fiber to the entrance 33-O of through-holes 33.

FIG. 9 is an exploded view of an exemplary embodiment of the presentinvention, in this case also illustrating various strain relief that maybe used in conjunction with the inventive 2D fiber array component. Theparticulars of the elements forming the inventive 2D array component 30itself are as described above. Also shown in FIG. 9 is an exemplarystrain relief configuration 70. In this particular embodiment,configuration 70 includes a plurality of small shrink tubes 72, eachtube disposed around a separate 1×N fiber array (in this case, in theform of a bare fiber ribbon 74). A larger shrink tube 76 is used toattach each separate ribbon 74 to an associated larger fiber tube 78.The shrink tubes are bonded to both fiber ribbon 74 and fiber guideblock 32, and function to “grab” the fiber ribbon and maintain theconnection to the guide block in the event that there is an attempt topull the fiber ribbon out of the assembly.

A glue block 80 is used to secure the plurality of fiber tubes 78 inplace (where only one half of glue block 80 is shown in FIG. 9). Astrain-relief cover plate 82 (shown as two portions 82-1 and 82-2) ispositioned to encase glue block 80 and the remaining components ofstrain relief arrangement 70, where the final combination is shown inposition at rear opening 46 of mounting flange 38. An assembled versionof this embodiment is shown in FIG. 10. By bonding the ribbons into glueblock 80 and then containing those elements within cover plate 82, theribbons are fixed in place such that handling the ribbons never pulls onthe stripped fibers inside, i.e. providing “strain relief”.

FIG. 11 is an exploded view of an alternative embodiment of the presentinvention. In this configuration, the fiber guide block of theabove-described embodiment is integrated as part of a mounting flange 90that is used to provide mechanical support for precision output element34. Here, a plurality of through-holes 92 are directly formed (e.g.,machined) in a desired 2D array pattern through a thickness of mountingflange 90 so as to exit at a top surface 94 of mounting flange 90.Similar to through-holes 33, the plurality of through-holes 92 areformed to exhibit the desired pitch P, while having a somewhat largerdiameter than apertures 36 (i.e., able to accept coated optical fibers).As shown in FIG. 11, the same precision output element 34 can be used inthis embodiment to provide the necessary precision (pitch and pointing)for the 2D fiber array assembly.

The formation of through-holes 92 directly in mounting flange 90eliminates the need for a separate fiber guide block, but at the cost ofincreasing the size and fabrication complexity of the mounting flange. Aprecision loading tool is again used to introduce 1×N fiber arrays(pre-aligned) into the structure.

FIG. 12 is an isometric view of output element 34 and mounting flange90, with this view illustrating an exemplary preferred configuration ofmounting flange 90 for supporting output element 34. As shown, mountingflange 90 is formed to include a recessed central region 96 which issized to support output element 34 in a manner whereby output element 34is in alignment with through-holes 92. Also shown in this view is alanding ridge (also referred to as a “shoulder”) 98 upon which outputelement 34 is positioned and affixed. As discussed below, the thicknessof ridge 98 can be controlled to provide the desired gap spacing gbetween surface 94 (i.e., the exit surface of the fibers from thehousing element) and bottom layer 50 (for example) of a silicon-basedoutput element 34.

FIG. 13 is a rear isometric view mounting flange 90, illustrating oneexemplary technique for loading a 1×N fiber array 100 into an associatedarray of through-holes 92 (a close-up view of the insertion of exemplaryfibers through associated through-holes is also shown). Here, anexemplary tool 150 is used to support a plurality of N fibers in alinear array, with the pre-determined pitch P created between adjacentfibers. Once the fibers are loaded onto tool 150 (and affixed in their“pre-aligned,” position), tool 150 directs the array into the relativelylarge-sized lead-in end openings 92-O of through-holes 82. Once loaded,the 1×N array of fibers is bonded in place (on the backside of mountingflange 90), and another plurality of N fibers is loaded onto tool 150.

As mentioned above, a significant aspect of the present invention is theability to utilize a precision tool to hold a 1×N array of fibers in apre-aligned spacing (i.e., with the pre-defined pitch) as the fibers areloaded into the invention 2D fiber array component. The utilization of aprecision tool substantially reduces the accuracy required in theformation of the through-holes in the fiber guide block, and yet allowsfor the desired pitch and pointing error requirements to be met (if notexceeded). Since the tool can be used over and over again, its cost isnot embedded in the components of the final assembly, allowing for arelatively inexpensive 2D fiber array component to be formed.

A flow chart of an exemplary process useful in assembly a 2D fiber arraycomponent of the present invention is shown in FIG. 14. As shown, theprocess begins at step 100 with providing a suitable precision outputelement that has been manufactured in accordance with pre-defined pitchand pointing error requirements. A fiber guide block is also provided atthis step, with the block having apertures of the same pitch as theoutput element, but with slightly larger diameter openings (i.e., ableto accept a coated fiber as opposed to the stripped fiber endterminations passing through the output element).

Next, a mounting flange is prepared (step 110) to include an opening forholding the fiber guide block and output element in a mechanicallysecure, aligned manner. Following this, the fiber guide block isinserted in the mounting flange (step 120), and the output element isinserted over the fiber guide block in the mounting flange (step 130).

At this point in the process, shown as step 140, a plurality of Noptical fibers having stripped end terminations is loaded on a precisiontool that positions the fibers with the desired pitch (i.e., the samepitch as the output element). The precision tool is then insertedthrough the backside of the mounting flange (step 150), with thepre-aligned fibers passing through the fiber guide block and outputelement. The stripped end terminations of the fibers will be visiblethrough the apertures formed in the output element.

Once loaded, an epoxy (or other suitable bonding material) is applied tothe backside of the fiber guide block to hold the loaded 1×N array offibers in place. This is shown as step 160. The precision tool isremoved once the fibers are fixed in place. At this point in theprocess, a check is made (step 170) to see of all of the 1×N fiberarrays have been loaded in the 2D fiber array component. Presuming thereare still other 1×N fiber arrays to be loaded, the process returns tostep 140, where a new set of stripped fibers is loaded onto theprecision tool.

At the point in the process where all of the 1×N fiber arrays have beenloaded, another epoxy (or bonding) process is used (step 180) to affixthe protruding end terminations 100E of fibers in place with respect tothe output element. Once the bonding is fully cured, a final polishingoperation can be performed on the output surface (step 190).

While the above discussion describes exemplary embodiments and assemblymethods for a 2D fiber array component, it is to be understood thatthere are various alternatives that may occur to those skilled in theart. Various materials may be utilized in the formation of each of theelements forming the component, for example. These alternatives areconsidered to fall within the scope of the present invention, which islimited only by the scope of the claims appended hereto.

What is claimed is:
 1. A two-dimensional (2D) array component forsupporting a plurality of individual optical fibers in a 2Dconfiguration exhibiting a predetermined pitch, the array componentcomprising: a fiber guide block including a plurality of through-holesarranged in a array configuration exhibiting the predetermined pitch,the plurality of through-holes formed to guide fibers passingtherethrough and reduce pointing error, with each through-hole having afirst diameter sufficient to accommodate a coated optical fiber; asilicon-based output element including a plurality of vias etchedthrough a thickness of the silicon-based output element, the pluralityof etched vias arranged in the 2D array configuration exhibiting thepredetermined pitch, each etched via having a second diameter less thanthe first diameter, the second diameter on the order of a claddedoptical fiber; and a mounting flange for supporting the fiber guideblock and the silicon-based output element in an aligned configurationsuch that the 2D array component exhibits a pitch error no greater than±1 μm and a pointing error no greater than ±15 mrad.
 2. The 2D arraycomponent as defined in claim 1 wherein the silicon-based output elementcomprises a multilayer structure.
 3. The 2D array component as definedin claim 2 wherein the multilayer structure silicon-based output elementcomprises an output silicon layer including a first plurality of etchedvias arranged in the 2D array configuration exhibiting the predeterminedpitch, each etched via formed to exhibit the first diameter; and aninput silicon layer including a second plurality of etched vias arrangedin the 2D array configuration, the input silicon layer positioned inalignment with the output silicon layer such that they second pluralityof etched vias aligns with the first plurality of etched vias.
 4. The 2Darray component as defined in claim 3 wherein each etched via of thefirst and second pluralities of etched vias includes a larger lead-inopening to facilitate the insertion of optical fibers.
 5. The 2D arraycomponent as defined in claim 3 wherein the multilayer structuresilicon-based output element further comprises a silicon spacer disposedbetween the output and input silicon layers, the silicon spacerincluding a plurality of relief holes disposed in a 2D array patternthat aligns with the first and second pluralities of etched vias formedin the output and input silicon layers.
 6. The 2D array componentsdefined in claim 5 wherein the silicon spacer is formed to have athickness t selected to minimize pointing error in the 2D arraycomponent.
 7. The 2D array component as defined in claim 3 wherein thediameter of the etched vias formed in the input silicon layer is greaterthan the first diameter associated with the etched vias formed in theoutput silicon layer.
 8. The 2D array component as defined in claim 1wherein the mounting flange includes a central sleeve for engaging thefiber guide block and the silicon-based output element, the centralsleeve including a first shoulder rim for supporting the fiber guideblock and a second shoulder rim for supporting the silicon-based outputelement with a predefined gap spacing g between the first and secondshoulder rims.
 9. The 2D array component as defined in claim 1 whereinthe fiber guide block is formed of a plastic material.
 10. The 2D arraycomponent as defined in claim 9 wherein the fiber guide block comprisesa molded plastic material component.
 11. A two-dimensional (2D) arraycomponent for supporting a plurality of individual optical fibers in a2D configuration exhibiting a predetermined pitch, the array componentcomprising: a silicon-based output element including a plurality of viasetched through a thickness thereof, the etched vias arranged in the 2Darray configuration to exhibit the predetermined pitch, each etched viahaving a small diameter on the order of a stripped optical fiber; and amounting flange for supporting the silicon-based output element, themounting flange including a plurality of large diameter through-holesdisposed at the predetermined pitch and in alignment with the pluralityof etched vias, such that a 1×N array of pre-aligned optical fibersinserted through a rear opening of the mounting flange thereafter exitsfrom the silicon-based output element in a configuration that exhibitsthe predetermined pitch with a minimal pointing error.